With the development of display technology, the requirements for people on the display panel resolution are getting higher and higher. In the prior art, in order to improve the resolution of the display panel, the low-temperature polysilicon technology is often employed in the display panel, i.e., low-temperature polysilicon TFT display substrate, but the TFT substrate currently used is generally a top-gate TFT substrate, i.e. a gate of the TFT is fabricated at the top of the TFT structure; the top-gate TFT substrate has excellent electrical properties, but its reliability is low.
When the top-gate TFT substrate undergoes excimer laser annealing of the amorphous silicon during the manufacturing process, unavoidable protrusions are formed on the formed polysilicon layer, and the protrusions affect the interface quality between the gate insulating layer and the polysilicon layer, the breakdown voltage of the gate insulating layer is reduced, thereby the further reduction in the thickness of the gate insulating layer is limited.
In the prior art, a bottom-gate TFT substrate is also used in some display panels. However, in the prior art, when a bottom-gate TFT substrate is fabricated, it is necessary to etch the barrier layer on the polysilicon layer to expose the polysilicon layer of the source and drain electrodes, and then to perform an ion implantation to the polysilicon layer of the source and drain electrodes; through this method, the damage of polysilicon below the barrier layer will be caused and the defect thereof will be introduced when the barrier layer is etched, the polysilicon layer will be completely etched when it gets serious, thereby the display quality of the display panel is affected.